Conventionally, there have been widely used electronic apparatuses which are represented by a notebook type personal computer, a portable telephone, a portable information terminal, and the like, and which are excellent in portability. In many cases, such electronic apparatuses include, for convenience of carriage, a main unit, on the upper surface of which operation keys such as character keys and numerical keys are arranged, and an image display unit which has a display screen and which is openable and closable with respect to the main unit. In such electronic apparatuses, it is possible to obtain information through the display screen by operating the operation keys arranged on the upper surface of the main unit.
Further, in recent years, there has also been developed and commercialized an electronic apparatus that has a touch panel, and the like, incorporated therein so as to also be able to cope with a usage form in which an instruction input, and the like, to the electronic apparatus is performed by bringing a finger or a dedicated pen into contact with or close to the display screen so that the position of the finger or the dedicated pen is recognized without inputting through the key. As such an electronic apparatus, there are known, for example, a palm-sized portable information terminal having limited processing capability (see, for example, Japanese Laid-Open Patent Publication No. 2003-330590), a tablet-type personal computer (hereinafter abbreviated as tablet PC), and the like.
Further, as the tablet PC, in addition to a so-called pure tablet PC which has a display screen on the upper surface thereof and which is formed in a plate shape as a whole, there is also known a convertible type tablet PC which is configured to include an image display unit that may be freely opened and closed with respect to a main unit, and which is configured by connecting the image display unit and the main unit to each other by using a connecting section having a high degree of freedom, in such a manner that not only the opening and closing of the image display unit but also the front and rear rotation of the image display unit may be performed so as to obtain a state in which the image display unit is closed with the display screen facing upward, and which is convenient for the usage form that an instruction input, and the like, is performed with a finger or a dedicated pen (see, for example, Japanese Laid-Open Patent Publication No. 2004-53927).
Generally, in the convertible type tablet PC, various buttons are arranged at a side of the display screen, or images of various buttons are displayed on the display screen, in order to obtain good operability at the time when the tablet PC is set in the tablet mode in which the image display unit is closed with the display screen facing upward. As such buttons, there are known, for example, a button for scrolling the screen, a button for performing the same processing as the processing performed at the time when a Ctrl key, an Alt key and a Del key in a common keyboard are simultaneously depressed, a button for switching a direction of an entire image displayed in the display screen, a button to which a desired function may be assigned by an operator, a button corresponding to the Enter key in a common keyboard, and the like.
Further, for the convertible type tablet PC, the display screen size is desired to be increased in order to increase the amount of display information and to improve the operability, while the outside shape size of the tablet PC is also desired to be reduced in order to improve the portability. That is, the outside shape of the apparatus may not be made smaller than the display screen area, but the miniaturization is desired in the sense that the outside shape of the apparatus is reduced as much as possible to the ends of the display screen so that the area of the peripheral portion of the display screen is reduced as much as possible.
However, when the buttons are arranged at sides of the display screen as described above, it is necessary to reduce the display screen area in correspondence with the space in which the buttons are arranged. Further, in the case where the images of the buttons are displayed on the display screen, the display screen may be extended as close as possible to the end of the outside shape of the apparatus. However, the space to display the images of the buttons is needed on the display screen, and hence the area to display an image other than the images of the buttons is reduced. Further, in the case where the buttons are arranged at the sides of the display screen or where the images of the buttons are displayed on the display screen, when the tablet PC is in the notebook PC mode in which the image display unit is opened with respect to the main unit, and when the buttons are operated by a finger or a dedicated pen, a large rotation moment may be applied with the hinge rotatably supporting the image display unit as a rotation shaft, and thereby the image display unit may be unintentionally rotated.
Further, as an electronic apparatus configured to cope with such problem, there is proposed a convertible type tablet PC including an image display unit which is openable, closable and rotatable with respect to the main unit, the tablet PC being configured such that buttons and a fingerprint sensor are arranged at the left side of a keyboard arranged on the upper surface of the main unit, and such that when the tablet PC is in the tablet mode in which the image display unit is closed with the display screen being oriented upward, the buttons and the fingerprint sensor are exposed (see, for example, Japanese Design Registration No. 1279770).
According to the convertible type tablet PC proposed in Japanese Design Registration No. 1279770, the buttons and the fingerprint sensor which are arranged at the left side of the keyboard on the upper surface of the main unit may be used at the time when the tablet PC is in the tablet mode. Thus, it is possible to obtain good operability without the buttons being arranged at the side of the display screen arranged in the image display unit or without the images of buttons being displayed on the display screen. Therefore, it is possible to extend the display screen as close as possible to the end of the outside shape of the apparatus, and it is also possible to avoid a decrease of an area of the display screen for displaying an image by displaying the images of the buttons on the display screen. Further, in the case where the tablet PC is in the notebook PC mode in which the image display unit is opened with respect to the main unit, it is possible to avoid an unintentional rotation of the image display unit at the time when the tablet PC is operated with a finger or a dedicated pen.